Ans. (b)

Sol. There are two stores of nutrients reserve pool and cycling pool.

• The reservoir for gaseous type of nutrient and biogeochemical cycle (nitrogen and carbon cycle) exists in atmosphere while earth crust is the reservoir for sedimentry cycle.
• Whereas stratosphere ionosphere and lithosphere are the parts of atmosphere.

Ques. If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be

(a) Scavenger
(b) Tertiary producer
(c) Tertiary consumer
(d) Secondary consumer

Ans. (c)

Sol. Producer $\rightarrow \underset{\text { (Primary consumer) }}{\text { Ist Trophic level }} \rightarrow \underset{\text { (Secondary consumer) }}{| \text { Ind Trophic level }} \rightarrow \underset{\text { (Tertiary consumer) }}{\text { IIrr Throphic level }}$

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• Scavengers are the detrivores which feeds on the tissue of dead animals (e.g., vultures) and do not play role in carbon fixation.
• Producers fix the carbon dioxide which is passed through the different trophic level.

Ques. Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below $100 \mathrm{~mm}$

(a) Grassland
(b) Shrubby forest
(c) Desert
(d) Mangrove

Ans. (c)

Sol. In true desert biome rainfall is less than $100 \mathrm{~mm} /$ year, characterised by extremely hot days and cold nights.

• Evaporation from true desert alwaays exceeds 7-50 times the precipitation (rainfall).
• Desert ecosystem of biomes are more in Northerm hemisphere than Southern hemisphere.

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• Whereas Grassland ecosystem receives medium rain fall ranging from 25-75 cm/yr but evaporation rate is not higher than precipitation rate.

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• Shrubby forest receives rainfall $90-150 \mathrm{~cm} / \mathrm{yr}$.

• Mangrove forests receive annual rainfall ranging from $100-150 \mathrm{~cm} / \mathrm{yr}$.

• Thus, there options are wrong.

Ques. The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called

(a) Pelagic zone
(b) Benthic zone
(c) Lentic zone
(d) Littoral zone

Thinking Process

• On the basis of light availability, an aquatic habitat can be categorised into lettoral, limnetic profundal and benthic zone.

Ans. (d)

Sol. The littoral zone is the zone at the edge of a lake or ocean or in aquatic habitat which is alternatively exposed to air, hence, light is also available and immersed in water.

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• This costal zone is rich producers from surface to bottom, with a large number of brown and red alga attached at the zone.

• Different zones is an equatic ecosystem.

• Pelagic zone Any zone of water in a sea or lake that is neither close to bottom nor the shore is pelagic zone.

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• Benthic zone It is the bottom part of the water body (aphotic zone) light is not available here and it is dark.

• Microorganisms and benthic organisms are found in this zone.

• Lentic zone refers to standing or relatively still water in an equatie ecosystem.

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Different zones in an equatic ecosystem

Ques. Edaphic factor refers to

(a) Water
(b) Soil
(c) Relative humidity
(d) Altitude

Thinking Process

• Edaphic factor is type of abiotic factors, the other are termed as climatic factors.

Ans. (b)

Sol. Edaphic factor refers to soil like soil texture, background, mineral, its topography and $\mathrm{pH}$ value etc.

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• Water, relative humidity and altitude another abiotic components of an ecosystem but affects the climatic conditions hence are climatic factors.
• The variations in these factors affects the ecosystem and these factors are also the deciding factor of the different types of ecosystem found on earth.

Ques. Which of the following is an ecosystem service provided by a natural ecosystem?

(a) Cycling of nutrients
(b) Prevention of soil erosion
(c) Pollutant absorption and reduction of the threat of global warming
(d) All of the above

Ans. (d)

Sol. A natural ecosystem maintain its biotic and abiotic factors naturally.

• The products of ecosystem processes are called the ecosystem services.
• A healthy ecosystem provides a wide range of economic, environmented and aesthetic goods and services.
• The various ecosystem services provided by a natural ecosystem includes

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(i) Purify air and water

(ii) Migration of droughts and floods

(iii) Nutrient cycling

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(iv) Generation of fertile soil

(v) Maintenance of biodiverstity

(vi) Provide storage site for carbon

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(vii) Pollinate crops

(viii) Also provides aesthetic, cultural and spiritual valves

• Thus, all the above options are correct.

Ques. Name an organism found as secondary carnivore in an aquatic ecosystem.

Ans. In an aquatic ecosystem, food chain can be drawn as follows

• Producer (Phytoplankton) $\rightarrow$ Primary consumer (Zooplankton) $\rightarrow$ Secondary consumer (small fish and water beetle) (Ist to carnivore) $\rightarrow$ Tertiary consumer (Ilnd carnivore like large fish, water birds like fowl and duck).

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• So, the large fish and water birds like ducks and water fowls which are the tertiary consumers in an aquatic ecosystem occupy a position of secondary carnivore.

Ques. What does the base tier of the ecological pyramid represent?

Ans. The base tier of the ecological pyramids represent the producers or first trophic level in case of three ecological pyramids (i) Pyramid of number

(ii) Pyramid of biomass

(iii) Pyramid of energy

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Ques. Under what conditions would a particular stage in the process of succession revert back to an earlier stage?

Ans. Natural disturbances like fire, flood or any other natural disaster and anthropogen activities can revert back to an earlier stage of succession.

Ques. Arrange the following as observed in vertical stratification of a forest; Grass, Shrubby plants, Teak, Amaranths.

Ans. Vertical stratification (dispersion) of species in a forest ecosystem is arranged as grass (floor of forest) $\rightarrow$ Amaranthus $\rightarrow$ Shrubby plants $\rightarrow$ Teak (tree).

Ques. Name an omnivore which occurs in both grazing food chain and the decomposer food chain.

Ans. Cockroaches and crow are two omnivore, that are present in both grazing or predator and detritus food chain.

Ques. Justify the pitcher plant as a producer.

Ans. Pitcher plant (Napenthes) is an insectivores plant, which is chlorophyllus and capable of trapping solar radiations for chemical energy for photosynthesis.

• It is infectivorous plant which are produced in the soil lacking nitrogen thus to make up their nitrogen deficiency they trap insects.

Ques. Name any two organisms which can occupy more than one trophic level in an ecosystem.

Ans. Human being (man) and birds (sparrow) can be frequently seen in more than one trophic level, in an ecosystem.

Ques. In the North East region of India, during the process of jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation.

• How would you explain the regrowth of forest in ecological term?

Ans. Forests that are cleared by burning and left for regrowth will show secondary succession.

• Since, soil is already present, the buried seeds oen to germinate.
• Due to wind dispersal and some other natural forces, new seeds will be brought into the area and new species will colonise the forest again.

Ques. Climax stage is achieved quickly in secondary succession as compared to primary succession.

• Why?

Ans. The rate of ecological succession is quicker in secondary succession as compared to primary succession as the soil (substratum) is already available for further succession.

• While in primary succession, the succession starts from bare rocks.
• Which take time for first colonisation by plants as there is no nutrient holding mechanisms.

Ques. Among bryophytes, lichens and fern which one is a pioneer species in a xeric succession?

Ans. The species that invade a bare area are called pioneer species.

• In a xeric succession, the pioneer species are usually lichens then bryophytes which are succeeded by ferns and some other bigger plants.

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• Lichen produces lichen acid and carbonic acid which corrodes rock surface and release minerals required for growth.
• The corroded rock accumulate soil particle by wind and provides substrate for Bryophytes and ferms.

Ques. What is the ultimate source of energy for the ecosystems?

Ans. Solar radiation is the ultimate source of energy for the ecosystem except deep hydrothermal ecosystem.